The present invention relates in general to a corrugated plastic tubing which is electrically conductive. Such electrical conductivity is particularly desirable to dissipate static electricity when the tubing is used to conduct oxygen, thereby minimizing any fire hazard. However, conductive plastic tubings may be used for other purposes as well.
The tubing is externally corrugated, by means of an external helical bead, to provide the tubing with sufficient stiffness to avoid collapse while still maintaining flexibility by utilizing a relatively thin wall between convolutions of the bead.
Prior U.S. patents having some pertinence to the present invention are: 3,070,132 Sheridan 3,166,688 Rowand et al 3,290,426 Barrentine 3,532,580 Kanao 3,645,834 McCaffrey
Sheridan, Rowand et al, Barrentine and McCaffrey all disclose tubings or pipes of dielectric material having longitudinally extending, electrically conductive inserts. The formation of such inserts creates problems in the manufacture of the tubings, and the inserts, being relatively narrow, result in relatively long, circumferential dielectric paths for the transfer of static charges to the conductive inserts.
Kanao discloses a method and apparatus of forming a plastic tubing having thereon an external helical bead. FIG. 8 of Kanao shows a reinforcement 62' of an unspecified material embedded in the helical bead.
Also of interest is Steward patent application Ser. No. 469,234, filed May 13, 1974, assigned to the same assignee as this application, and a continuation of Ser. No. 284,944, filed Aug. 30, 1972, and now abandoned. Steward discloses a method and apparatus of forming a plastic tubing having thereon an external helical bead.